Convert Lat/Longs to X/Y Co-ordinates

后端未结

关注

 3  1627

不要未来只要你来

I have the Lat/Long value of New York City, NY; 40.7560540,-73.9869510 and a flat image of the earth, 1000px × 446px.

I would like to be able to convert, using Javas

相关标签:

3条回答

不知归路

2020-11-30 22:27

The projection you use is going to change everything, but this will work assuming a Mercator projection:

<html>
<head>
<script language="Javascript">
var dot_size = 3;
var longitude_shift = 55;   // number of pixels your map's prime meridian is off-center.
var x_pos = 54;
var y_pos = 19;
var map_width = 430;
var map_height = 332;
var half_dot = Math.floor(dot_size / 2);
function draw_point(x, y) {
    dot = '<div style="position:absolute;width:' + dot_size + 'px;height:' + dot_size + 'px;top:' + y + 'px;left:' + x + 'px;background:#00ff00"></div>';
    document.body.innerHTML += dot;
}
function plot_point(lat, lng) {
    // Mercator projection

    // longitude: just scale and shift
    x = (map_width * (180 + lng) / 360) % map_width + longitude_shift;

    // latitude: using the Mercator projection
    lat = lat * Math.PI / 180;  // convert from degrees to radians
    y = Math.log(Math.tan((lat/2) + (Math.PI/4)));  // do the Mercator projection (w/ equator of 2pi units)
    y = (map_height / 2) - (map_width * y / (2 * Math.PI)) + y_pos;   // fit it to our map

    x -= x_pos;
    y -= y_pos;

    draw_point(x - half_dot, y - half_dot);
}
</script>
</head>
<body onload="plot_point(40.756, -73.986)">
    <!-- image found at http://www.math.ubc.ca/~israel/m103/mercator.png -->
    <img src="mercator.png" style="position:absolute;top:0px;left:0px">
</body>
</html>

0 讨论(0)

遥遥无期

2020-11-30 22:35
A basic conversion function in js would be:
```
MAP_WIDTH = 1000;
MAP_HEIGHT = 446;

function convert(lat, lon){
    var y = ((-1 * lat) + 90) * (MAP_HEIGHT / 180);
    var x = (lon + 180) * (MAP_WIDTH / 360);
    return {x:x,y:y};
}
```
This will return the number of pixels from upper left. This function assumes the following:
1. That your image is properly aligned with the upper left corner (0,0) aligning with 90* North by 180* West.
2. That your coords are signed with N being -, S being +, W being - and E being +
0 讨论(0)
发布评论:

提交评论
- 加载中...
孤街浪徒

2020-11-30 22:39

If you have a picture of the whole earth, the projection does always matter. But maybe I just don't understand your question.

0 讨论(0)
发布评论:

提交评论
- 加载中...